The present invention relates to a method and apparatus for the concentration of gases and vapours present in trace quantities in the atmosphere or in some other gaseous medium. In this specification the gases and vapours which are of interest will be referred to as "vapours". Such vapours normally are gaseous forms of materials which may be gaseous, liquid or solid at room temperature, or those which are emitted from liquids and solids at room temperature. They will also embrace in this connection certain gases which are not considered vapours but which are capable of being adsorbed onto adsorption powders for removal from an air stream or the like.
Specifically the invention relates to a device and method for enhancing the concentration of trace gases and vapours to such a level that they may be more readily analyzed by appropriate instrumentation.
A great deal of work has been done in recent years to facilitate the work of detecting bombs in various situations, such as in maintaining security at airports and in boarding aircraft. X-ray machines and manual searches are, of course, invaluable but cannot be expected to detect all types of weapons such as explosives.
The devices already known involve the preconcentration of vapours in discrete volumes of air. A measured volume of sample air is passed through a solid or liquid filter which collects the vapours of interest. The collected vapours are subsequently retrieved in a much more concentrated form than originally prevailing in the atmosphere. If the volume of air sampled is large enough, sufficient vapour may be recovered to be amenable to analysis. This basically constitutes a batching-sample method and is therefore time consuming and generally unsuitable for real time requirements.
In U.S. Pat. No. 2,493,911, issued on Jan. 10, 1950, to P. L. Brandt, an adsorption powder is continuously recirculated through cool adsorption and hot desorption regions to effect separation of the desired components. The process described by Brandt requires relatively large quantities of adsorbent powder for its industrial applications, and it is relatively expensive to use. The large amount of powder involved also places a constraint on the speed of operation of the adsorption-desorption process. The Brandt patent relies on the evolution of relatively large quantities of gas during the desorption phase to transport the adsorption powder from a low to a high elevation, which would not be effective when attempting to separate and concentrate minute traces of gases from the mixture as in the present invention.
Also known in the prior art is the use of a cyclone separator to remove naturally prevailing dust particles in the atmosphere for the purpose of subjecting them to elemental analysis. This is used in geographical surveys and has been developed, for example, by Barringer Research Limited of Toronto, Canada, (see U.S. Pat. No. 3,998,734 issued Dec. 21, 1976, of A. R. Barringer).
The present inventor has been involved in an ongoing research programme to develop the present invention, as summarized in the proceedings of "New Concepts Symposium and Workshop", Oct. 30 to Nov. 1, 1978, Reston, Virginia, U.S.A., published by The U.S. Departments of Treasury, Energy, Justice and Transportation, pages 265 to 267, the contents of which are incorporated herein by reference.